1. Field of the Invention
This invention relates to a "negative-type" resist material capable of being processed under visible light or normal room illumination, which is curable by irradiation with high energy radiation such as electron beams, X-rays, ion beams, .beta.-rays, .gamma.-rays, neutron beams and deep ultraviolet light but is substantially non-curable by irradiation with light having a wavelength of about 300 nm or more. More particularly, the present invention relates to a resist material for microworking of mainly superhigh density integrated circuits and various other devices in the electronics industry.
2. Description of the Prior Art
Two types of resist materials for high energy radiation are known. One type is a so-called positive type resist material in which the irradiated areas decompose and become solvent-soluble, and the other type is a negative type resist material, in which the resist material of this invention operates in a similar manner, in that the irradiated areas are cured and become solvent-insoluble.
Poly(methyl methacrylate) has long been known as a positive type resist material. Poly(methyl methacrylate) has very excellent resolution properties, but the sensitivity thereof is very low, thus, it is very disadvantageous for practical use (e.g., as disclosed in I. Haller et al., IBM J. Res & Develop., 12, 251 (1968)). Further, poly(butene-1 sulfone) has a sufficiently high sensitivity but has inferior resolution properties and is quite poor in anti-ion etching property (e.g., as disclosed in M. J. Bowden et al., J. Vac. Sci. & Technol., 12, 1294 (1975)).
On the other hand, poly(glycidyl methacrylate-CO-ethyl acrylate) is known as a negative type resist material (e.g., as disclosed in L. F. Thompson et al., Polymer Eng. Sci., 14, 529 (1974)). This material has sufficient sensitivity, e.g., as high as 10.sup.-7 coulomb/cm.sup.2, but does not have sufficient resolution properties. Namely, this material is not practically applicable for pattern formation of less than 1.mu.. Further, the heat stability of this resist material is low, and even if prebaking is carried out at 80.degree. C. for 30 minutes using this resist material, heat fog takes place.
In addition, poly(diallyl phthalate) having good heat stability and anti-plasma etching properties is known as a negative type resist material. However, this material has a low sensitivity (e.g., as disclosed in J. L. Bartlett, Appl. Polymer Symposium, No. 23, 139 (1974)).
In view of the above, no resist materials are known which are free of problems in all areas of sensitivity, resolution properties, storage stability and heat stability.
Recently, application of lithography using short-wavelength radiation such as electron beams, X-rays and vacuum ultraviolet light has been extensively studied incident to the higher degree of integration of semiconductor integrated circuits or the production of sonic wave elements of an ultrafine structure, magnetic bubble memories, etc.
Radiation-polymerizable and insolubilizable compounds are well known in the art as radiation-curable or negative resist materials.
Typically, a negative resist material is dissolved in a suitable solvent, and the solution is coated on the surface of a substrate. The solvent is evaporated off to form a resist film on the surface. The resist film is then exposed to radiation to cure the resist film in the exposed portion. The unexposed portion is removed with a solvent to form a resist image. The portion of the substrate not covered by the cured film is processed by, for example, etching or impurity doping, and the cured film is removed chemically or by plasma etching.
Some known conventional negative resist materials have sufficiently high sensitivity for practical applications. Generally, however, the resolving power and stability of negative resist materials tend to decrease as their sensitivity increases. Really practical negative resist materials which have satisfactory sensitivity, resolving power and stability are not yet known as can be seen from the above.
Further, many types of resist materials must be employed using several types of methods in order to attain superior adhesion to the surfaces of various substrates, for example, substrates of a non-metal or non-metal compound such as silicon, silicon oxide or silicon nitride, a metal or metal compound such as chromium, aluminum, gold, or chromium oxide, or a rare earth compound or a rare earth element composite, and to obtain superior resistance to etching as well as high sensitivity and high resolution which is desirable. Detailed investigations have now led to a resist material having a high level of practical applicability that can meet these requirements and the present invention has been accomplished.